An important problem encountered in today's information technology (IT) environment is known as server sprawl. Because of unplanned growth, many data centers today have large numbers of heterogeneous servers, each hosting one application and often grossly under utilized.
A solution to this problem is a technique known as server consolidation. In general, server consolidation involves converting each physical server or physical machine into a virtual server or virtual machine (VM), and then mapping multiple VMs to a physical machine, thus increasing utilization and reducing the required number of physical machines.
There are some critical runtime issues associated with a consolidated server environment. For example, due to user application workload changes or fluctuations, a critical problem often arises in these environments. The critical problem is that end user application performance degrades due to over utilization of critical resources in some of the physical machines. Accordingly, an existing allocation of VMs to physical machines may no longer satisfy service level agreement (SLA) requirements. As is known, an SLA is an agreement between a service customer (e.g., application owner) and a service provider (e.g., application host) that specifies the parameters of a particular service (e.g., minimum quality of service level). As a result, VMs may need to be reallocated to other physical machines. However, such a reallocation has an associated migration cost. Existing consolidation approaches do not account for the cost of migration.